Add store into existing web site

I have a client who has an existing website, that they would like to sell products from now. Can Zen Cart be embedded into their existing site,
since customizing the Zen Cart to match doesn't seem to be all that easy. I've been able to get close in the past, but not completely.
Can you please point me to a tutorial on how to accomplish this if it can be done?
Thank you.

There is no styling tutorial I'm aware of. Matching an existing site is mostly a matter of trial and error.

If we could see the existing site, we might be able to offer some advice.

You can look at the free templates available for Zen Cart and see if any of them give you a head start on matching the current design. http://(sorry, site offline)/ Use the pull down menu to see what the templates look like on a live site.

Plus, as Steve suggested, a link to the current site will give folks a better idea of what you're trying to do.